Time division modulation with average current regulation for independent control of arrays of light emitting diodes

ABSTRACT

Exemplary apparatus, method and system embodiments provide for separately and independently sourcing current to a series of light emitting diodes of a plurality of series of light-emitting diodes. An exemplary apparatus comprises a power converter which generates a current, a first multiplexer, and a controller. The controller provides for sequential and separate switching of the current through the first multiplexer to each of the series of light-emitting diodes for a corresponding period of time. An average current provided by the power converter is determined as substantially equal to a sum of the corresponding currents through the plurality of series of light-emitting diodes. A total period for switching current to all of the series of light-emitting diodes is also determined. A corresponding time period for switching current to a selected corresponding series of light-emitting diodes is substantially equal to a proportion of the total period determined as a ratio of the corresponding current for the selected corresponding series of light-emitting diodes to the average current provided by the power converter.

FIELD OF THE INVENTION

The present invention in general is related to converters and regulatorsused for driving and controlling arrays of light emitting diodes and, inparticular, is related to an apparatus, system and method for timedivision modulation with average current regulation for independentcontrol of arrays of light emitting diodes.

BACKGROUND OF THE INVENTION

Arrays of light emitting diodes (“LEDs”) are utilized for a wide varietyof applications, including for ambient lighting. To achieve emission oflight perceived as white light, LED arrays typically utilize acombination of red, green and blue (“RGB”) LEDs (and, occasionally,amber LEDs), usually as a first series connection (a first “string”) ofa plurality of red LEDs, a second series connection (a second string) ofa plurality of green LEDs, and a third series connection (a thirdstring) of a plurality of blue LEDs, typically which are referred to as“multistring LEDs”.

For driving an array of LEDs, electronic circuits typically employ aconverter to transform an AC input voltage (e.g., “AC mains”) andprovide a DC voltage source, with a linear regulator then used toregulate LED current. For example, in Mueler et al., U.S. Pat. No.6,016,038, entitled “Multicolored LED Lighting Method and Apparatus”,the LEDs may be controlled by a processor to alter the brightness and/orcolor of the generated light, such as by using pulse-width modulated(“PWM”) signals.

Multistring LED Drivers with PWM regulation are known, e.g., SubramanianMuthu, Frank J. P. Schuurmans, and Michael D. Pashly “Red, Blue, andGreen LED for White Light Illumination”, IEEE Journal on Selected Topicsin Quantum Electronics, Vol. 8, No. 2, March/April 2002, pp. 333-338.Such prior art multistring LED drivers typically require redundantdrivers for every LED string. For example, in the prior art systemillustrated in FIG. 1, three separate and independent flyback converters10 operating at a constant switching frequency of 100 kHz drive acorresponding string of an RGB LED light source 15, with a PWM 20driving scheme operating at a frequency of 120 Hz. Each flybackconverter 10 contains a current loop to maintain a constant peak currentfor the PWM pulses. The color control system is implemented in a DSPcontroller 25 (TMS320F240), which supplies the PWM turn-on and turn offsignals for the power supply.

A similar prior art approach using redundant drivers for multistringLEDs is suggested in Chang et al., U.S. Pat. No. 6,369,525, entitled“White Light-Emitting-Diode Lamp Driver Based on Multiple OutputConverter with Output Current Mode Control”, which utilizes a white LEDarray driver circuit with a multiple output flyback (or forward)converters with output current mode control, as illustrated in FIG. 2.The circuit 40 comprises a power supply source, and a transformer havinga primary winding 41 and multiple secondary windings 42, with eachlight-emitting-diode string coupled in the circuit to one of thesecondary windings. A main controller 43 is coupled to a first of thelight-emitting-diode strings 46 and is configured to control a flow ofcurrent to the primary transformer winding 41. The circuit alsocomprises an additional plurality of secondary controllers 44, 45, eachof which is correspondingly coupled to another light-emitting-diodestring 47, 48 to control a flow of current to its correspondinglight-emitting-diode string.

An analog implementation of this teaching can be found in the AS3691product from Austriamicrosystems (LEDs Magazine 2005). The AS3691includes four independent high precision current sources each capable ofsinking 400 mA. The operating current per LED channel can be set via anexternal resistor, while the LED brightness is controlled by fourindependent pulse width modulated inputs. The AS3691 integrates fourindependent current sinks per chip, enabling it to drive either fourwhite LEDs each sinking 400 mA or a single white LED with up to 1.6 A.

Another prior art method utilizes multiple, separate linear regulators,with each regulator separately coupled to an LED string of an LED array.For example, an AC-to-DC converter, for transforming AC input voltageinto a DC voltage source, is coupled to multiple, dedicated linearregulators, with one regulator coupled to each LED string to regulatethe current in that corresponding LED string. This approach represents amultistage power system with low efficiency of power conversion, inaddition to already low efficiency of series pass current regulators,particularly when the DC voltage is constant and does not depend oncurrent. This prior art method of multiple and separate linearregulators is illustrated in the following U.S. Pat. No. 7,064,498Light-Emitting Diode Based Products; U.S. Pat. No. 7,038,399 Methods AndApparatus For Providing Power To Lighting; U.S. Pat. No. 6,965,205 LightEmitting Diode Based Products; U.S. Pat. No. 6,806,659 Multicolored LEDLighting Method And Apparatus; U.S. Pat. No. 6,801,003 Systems AndMethods For Synchronizing Lighting Effects; U.S. Pat. No. 6,788,011Multicolored LED Lighting Method And Apparatus; U.S. Pat. No. 6,720,745Data Delivery Track; U.S. Pat. No. 6,636,003 Apparatus And Method ForAdjusting The Color Temperature Of White Semiconductor Light Emitters;U.S. Pat. No. 6,624,597 Systems And Methods For Providing IlluminationIn Machine Vision Systems; U.S. Pat. No. 6,548,967 Universal LightingNetwork Methods And Systems; U.S. Pat. No. 6,528,954 Smart Light Bulb;U.S. Pat. No. 6,459,919 Precision Illumination; U.S. Pat. No. 6,340,868Illumination Components; U.S. Pat. No. 6,292,901 Power/Data Protocol;U.S. Pat. No. 6,211,626 Illumination Components; U.S. Pat. No. 6,166,496Lighting Entertainment System; and U.S. Pat. No. 6,150,774 MulticoloredLED Lighting Method And Apparatus.

Similarly, in U.S. Pat. No. 6,016,038, entitled “Multicolored LEDLighting Method and Apparatus”, each LED string of the LED array iscontrolled by a separate current regulator with a processor, to alterthe brightness and/or color of the generated light using pulse-widthmodulated signals. In this case, an additional, current sink stage isadded in series with each LED string current regulator, resulting in afurther decrease in efficiency, particularly when the current sink isused to bypass the LED current to ground when the LED should be off.This multistage power system, with dedicated current converters andcontrollers in each LED channel, in addition to low efficiency, has alarge size, many expensive components, and is expensive to manufacture.

Lastly, in Archenhold et al. U.S. Pat. No 6,963,175, entitled“Illumination Control System”, a light emitting diode illuminationcontrol system is disclosed for driving a current circuit for energizingone or more LED light sources. The system comprises a control systemincluding a microprocessor, arranged to control a pulse amplitudemodulated (PAM) voltage controlled current circuit, and may employ amonitor for monitoring at least one ambient condition and amicroprocessor operable to control the current circuit to response tothe monitored conditions. This proposal has several significantproblems: (1) the system is very complex, inefficient (for powerconversion), has many expensive components, and is expensive tomanufacture; (2) the current to emission (color) transfer function inemitting diodes is substantially nonlinear, leading to a poor colorcontrol or requiring additional, undisclosed technical means forcompensation of this nonlinearity (not suggested in the patent); and (3)the disclosed current source operates poorly, suffering from thermaldependency and requiring correction by a microprocessor.

The referenced prior art with multi-output or separate power convertersand controllers for each LED string of an LED array increases the costand size of the LED driver, and reduces the functionality and efficiencyof the driver. Accordingly, a need remains for a multistring LED driverwhich utilizes a single power converter and controller for an entire LEDarray and does not utilize these multiple, separate power converters andcontrollers for each LED string. Such a multistring LED driver shouldprovide for independent current control for each LED string of thearray, for corresponding effective color and brightness control. Inaddition, such an LED array driver should provide for local LEDregulation, providing local compensation of LED emission due to age anddrift of functional parameters, temperature changes of the LED junction,LED production characteristics variation, and variations of devicesproduced by different manufacturers. Such an LED array driver alsoshould be backwards-compatible with legacy LED control systems.

SUMMARY OF THE INVENTION

As discussed in greater detail below, the various embodiments of theinvention provide innumerable advantages for energizing a plurality ofseries (strings) of LEDs, using a single power converter and controllerfor an entire LED array, and does not utilize multiple, separate powerconverters and controllers for each LED string. The exemplaryembodiments provide a multistring LED driver which controls currentindependently for each series of LEDs of the array, for correspondingeffective color and brightness control, among other features. Inaddition, the exemplary LED array drivers provide for local LEDregulation, achieving local compensation of LED emission due to age anddrift of functional parameters, temperature changes of the LED junction,LED production characteristics variation, and variations of devicesproduced by different manufacturers. The exemplary LED array drivers arealso backwards-compatible with legacy LED control systems.

Providing such local regulation of LED arrays is a significant advancecompared to the prior art use of a central, overall system (or host)computer or microprocessor for certain types of remote regulation. Thelocal regulation provided by the present invention enables asignificantly faster response time, without requiring the prior artcommunication protocols, and further provides a more comprehensiveapproach for maintaining selected color and brightness levels throughoutthe life span of the LEDs and corresponding changes in their functionalparameters. Exemplary embodiments also may be implemented usingcomparatively lower cost controllers. When the exemplary embodiments arefurther implemented to be backwards-compatible with legacy controlsystems, the present invention frees the host computer for other tasksand allows such host computers to be utilized for other types of systemregulation.

An exemplary apparatus embodiment, for providing current independentlyto a series of light emitting diodes of a plurality of series oflight-emitting diodes, comprises a power converter, a first multiplexer,and a controller. The power converter is couplable to the plurality ofseries of light-emitting diodes, and the power converter is adapted togenerate a current. The first multiplexer is also couplable to theplurality of series of light-emitting diodes. The controller is coupledto the power converter and to the first multiplexer, and the controlleris adapted to provide for sequential and separate switching of thecurrent through the first multiplexer to each of the series oflight-emitting diodes, of the plurality of series of light-emittingdiodes, for a corresponding period of time. The controller is furtheradapted to provide for no switching of current through the firstmultiplexer to all remaining series of light-emitting diodes whilecurrent is switched to a selected series of light-emitting diodes of theplurality of series of light-emitting diodes.

In exemplary embodiments, the controller is further adapted to determinean average current provided by the power converter as substantially orabout equal to a sum of a plurality of corresponding currents throughthe plurality of series of light-emitting diodes, and to determine atotal period for switching current to all of the series oflight-emitting diodes of the plurality of series of light-emittingdiodes. The controller may also be adapted to determine a correspondingtime period for switching current to a selected corresponding series oflight-emitting diodes as substantially (or about) equal to a proportionof the total period determined as a ratio of the corresponding currentfor the selected corresponding series of light-emitting diodes to theaverage current provided by the power converter.

An exemplary apparatus embodiment may further include a memory coupledto the controller, with the memory adapted to store, as a look up table,a plurality of parameters corresponding to the plurality of series oflight-emitting diodes. In exemplary embodiments, the controller isfurther adapted to predict an output voltage across a selected series oflight-emitting diodes based on the device parameters stored in memoryand to revise the predicted output voltage based upon a measured outputvoltage across a selected series of light-emitting diodes.

The power converter may further comprise a first voltage divider, withthe controller being further adapted to determine an input voltageacross the first voltage divider. Similarly, the power converter mayfurther comprise a current sensor, with the controller being furtheradapted to determine a peak input current through the current sensor. Inaddition, exemplary embodiments may also include a plurality ofcapacitors, with each capacitor of the plurality of capacitors couplableto a corresponding series of light-emitting diodes of the plurality ofseries of light-emitting diodes.

An exemplary apparatus embodiment may further include a plurality ofsecond voltage dividers, with each second voltage divider couplable inparallel to a corresponding series of light-emitting diodes of theplurality of series of light-emitting diodes, with the controller beingfurther adapted to determine a corresponding output voltage across thecorresponding second voltage divider of the plurality of second voltagedividers. In exemplary embodiments, a second multiplexer may be coupledto the plurality of second voltage dividers and the controller, with thecontroller being further adapted to control switching of the secondmultiplexer to a selected second voltage divider of the plurality ofsecond voltage dividers. Also in exemplary embodiments, a thirdmultiplexer may be couplable to the plurality of series oflight-emitting diodes and coupled to the controller, with the controllerbeing further adapted to control switching of the third multiplexer to aselected series of light-emitting diodes of the plurality of series oflight-emitting diodes for measuring a corresponding current through theselected series of light-emitting diodes.

In various exemplary embodiments, the controller may be further adaptedto determine the corresponding period of time for switching of currentto a selected series of light-emitting diodes based on a comparison ofthe measured corresponding current to a predetermined current level forthe selected series of light-emitting diodes. In other embodiments, thecontroller may be further adapted to determine the corresponding periodof time for switching of current to a selected series of light-emittingdiodes based on an integer multiple of a period of switching of thepower converter, and may be further adapted to control switching of thefirst multiplexer to a selected series of light-emitting diodes of theplurality of series of light-emitting diodes when current through thepower converter is substantially (or about) zero.

In various exemplary embodiments, the controller may be further adapted,in response to a first input, to adjust an output brightness of theplurality of series of light-emitting diodes by modifying eachcorresponding period of time of current switching to each of the seriesof light-emitting diodes. In addition, the controller may be furtheradapted, in response to a second input, to adjust an output color of theplurality of series of light-emitting diodes by modifying at least onecorresponding period of time of current switching to at least one of theseries of light-emitting diodes of the plurality of series oflight-emitting diodes.

In exemplary embodiments, the first multiplexer may comprises aplurality of switches, with each switch of the plurality of switchescorrespondingly couplable to a first, high side of a correspondingseries of light-emitting diodes of the plurality of series oflight-emitting diodes, or couplable to a second, low side of acorresponding series of light-emitting diodes of the plurality of seriesof light-emitting diodes. In other embodiments, the first multiplexermay comprise a plurality of first switches, with each switch of theplurality of first switches correspondingly couplable to a first, highside of a corresponding series of light-emitting diodes of the pluralityof series of light-emitting diodes; and a plurality of second switches,with each switch of the plurality of second switches correspondinglycouplable to a second, low side of a corresponding series oflight-emitting diodes of the plurality of series of light-emittingdiodes. In yet other embodiments, the first multiplexer may comprises aplurality of first switches, with each switch of the plurality of firstswitches correspondingly couplable to a first, high side of acorresponding series of light-emitting diodes of the plurality of seriesof light-emitting diodes; and a second switch couplable to the pluralityof capacitors.

In exemplary embodiments, a lighting system comprises a plurality ofseries of light-emitting diodes, a power converter, a first multiplexer,and a controller. The power converter is coupled to the plurality ofseries of light-emitting diodes and is adapted to generate a current.The first multiplexer is coupled to the plurality of series oflight-emitting diodes. The controller is coupled to the power converterand to the first multiplexer, and the controller is adapted to providefor sequential and separate switching of the current through the firstmultiplexer to each of the series of light-emitting diodes, of theplurality of series of light-emitting diodes, for a corresponding periodof time.

The exemplary embodiments further provide a method of selectively andindependently providing power to a series of light emitting diodes of aplurality of series of light-emitting diodes. The method comprisesgenerating an input DC current having a first average level; andsequentially and separately switching the DC current to each of theseries of light-emitting diodes, of the plurality of series oflight-emitting diodes, for a corresponding period of time. The exemplarymethod may further include switching no current to all remaining seriesof light-emitting diodes while switching the DC current to a selectedseries of light-emitting diodes of the plurality of series oflight-emitting diodes.

In exemplary embodiments, the method may also include determining thefirst average level of DC current as substantially or about equal to asum of a plurality of corresponding currents through the plurality ofseries of light-emitting diodes, determining a total period forswitching current to all of the series of light-emitting diodes of theplurality of series of light-emitting diodes, and determining acorresponding time period for switching current to a selectedcorresponding series of light-emitting diodes as substantially or aboutequal to a proportion of the total period determined as a ratio of thecorresponding current for the selected corresponding series oflight-emitting diodes to the average current provided by the powerconverter. An exemplary method may also include storing, as a look uptable, a plurality of parameters corresponding to the plurality ofseries of light-emitting diodes, and predicting an output voltage acrossa selected series of light-emitting diodes, of the plurality of seriesof light-emitting diodes, based on the stored device parameters. Theexemplary method may further include measuring a corresponding outputvoltage for each series of light emitting diodes of the plurality ofseries of light-emitting diodes; updating the predicted output voltageacross a selected series of light-emitting diodes, of the plurality ofseries of light-emitting diodes, based on a corresponding measuredoutput voltage; determining an input voltage; determining a peak inputDC current; determining a corresponding output voltage for each seriesof light emitting diodes of the plurality of series of light-emittingdiodes; and/or measuring a corresponding current through each series oflight-emitting diodes of the plurality of series of light-emittingdiodes.

In other exemplary embodiments, the method may include determining thecorresponding period of time for switching of current to a selectedseries of light-emitting diodes based on a comparison of the measuredcorresponding current to a predetermined current level for the selectedseries of light-emitting diodes, and/or determining the correspondingperiod of time for switching of current to a selected series oflight-emitting diodes based on an integer multiple of a period ofswitching of a power converter. In addition, the method may includeswitching current to a selected series of light-emitting diodes of theplurality of series of light-emitting diodes when the input DC currentis substantially (or about) zero.

Another exemplary embodiment provides an apparatus for providing currentindependently to a series of light emitting diodes of a plurality ofseries of light-emitting diodes, with the apparatus comprising a powerconverter, a first multiplexer, a memory, and a controller. The powerconverter is couplable to the plurality of series of light-emittingdiodes and is adapted to generate a current. The first multiplexer isalso couplable to the plurality of series of light-emitting diodes. Thememory is adapted to store, as a look up table, a plurality ofparameters corresponding to the plurality of series of light-emittingdiodes. The controller is coupled to the power converter, to the firstmultiplexer and to the memory, with the controller being adapted toprovide for sequential and separate switching of the current through thefirst multiplexer to each of the series of light-emitting diodes, of theplurality of series of light-emitting diodes, for a corresponding periodof time; the controller further adapted to determine an average currentprovided by the power converter as substantially or about equal to a sumof a plurality of corresponding currents through the plurality of seriesof light-emitting diodes, to determine a total period for switchingcurrent to all of the series of light-emitting diodes of the pluralityof series of light-emitting diodes, and to determine a correspondingtime period for switching current to a selected corresponding series oflight-emitting diodes as substantially or about equal to a proportion ofthe total period determined as a ratio of the corresponding current forthe selected corresponding series of light-emitting diodes to theaverage current provided by the power converter.

Numerous other advantages and features of the present invention willbecome readily apparent from the following detailed description of theinvention and the embodiments thereof, from the claims and from theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will bemore readily appreciated upon reference to the following disclosure whenconsidered in conjunction with the accompanying drawings, wherein likereference numerals are used to identify identical components in thevarious views, and wherein reference numerals with alphabetic characters(with or without subscripts) are utilized to identify particularinstantiations of a corresponding type of selected component in thevarious views, in which:

FIG. 1 (or FIG. 1) is a prior art LED array driver.

FIG. 2 (or FIG. 2) is a prior art LED array driver.

FIG. 3 (or FIG. 3) is a circuit and block diagram illustrating a firstexemplary LED array driver circuit in accordance with the teachings ofthe present invention.

FIG. 4 (or FIG. 4) is a timing diagram for a first exemplary LED arraydriver circuit in accordance with the teachings of the presentinvention.

FIG. 5 (or FIG. 5) is a diagram illustrating continuous current in aninductor in a first exemplary LED array driver circuit in accordancewith the teachings of the present invention.

FIG. 6 (or FIG. 6) is a diagram illustrating discontinuous current in aninductor in a first exemplary LED array driver circuit in accordancewith the teachings of the present invention.

FIG. 7 (or FIG. 7) is a circuit and block diagram illustrating a secondexemplary LED array driver circuit in accordance with the teachings ofthe present invention.

FIG. 8 (or FIG. 8) is a circuit diagram illustrating high side drivingand low side sensing of a series of LEDs in accordance with theteachings of the present invention.

FIG. 9 (or FIG. 9) is a circuit diagram illustrating differential highside sensing and low side driving of a series of LEDs in accordance withthe teachings of the present invention.

FIG. 10 (or FIG. 10) is a graphical diagram illustrating simulation of aboost LED array driver circuit, for three series of LEDs, in accordancewith the teachings of the present invention.

FIG. 11 (or FIG. 11) is a circuit diagram illustrating a firstconfiguration of an LED array for independent time division modulationin accordance with the teachings of the present invention.

FIG. 12 (or FIG. 12) is a circuit diagram illustrating a secondconfiguration of an LED array for common time division modulation inaccordance with the teachings of the present invention.

FIG. 13 (or FIG. 13) is a graphical diagram illustrating simulation ofLED current in a boost LED array driver circuit, for three LED strings,in accordance with the teachings of the present invention.

FIG. 14 (or FIG. 14) is a flow diagram illustrating an exemplary methodin accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

While the present invention is susceptible of embodiment in manydifferent forms, there are shown in the drawings and will be describedherein in detail specific exemplary embodiments thereof, with theunderstanding that the present disclosure is to be considered as anexemplification of the principles of the invention and is not intendedto limit the invention to the specific embodiments illustrated. In thisrespect, before explaining at least one embodiment consistent with thepresent invention in detail, it is to be understood that the inventionis not limited in its application to the details of construction and tothe arrangements of components set forth above and below, or asdescribed and illustrated in the drawings. Apparatuses consistent withthe present invention are capable of other embodiments and of beingpracticed and carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein, as well as theabstract included below, are for the purposes of description and shouldnot be regarded as limiting.

Referring now to the Figures, wherein like reference numerals are usedto identify identical components in the various views, and whereinreference numerals with alphabetic characters (with or withoutsubscripts) are utilized to identify particular instantiations of acorresponding type of selected component in the various views, FIG. 3 isa circuit and block diagram illustrating a first exemplary LED arraydriver circuit 100 in accordance with the teachings of the presentinvention. The first exemplary LED array driver circuit 100 comprises a(switching) power converter 120, a parallel array of LEDs 110, amultiplexer (or other array of power switches) 150 (typically referredto as a first, time-division multiplexer 150), a controller 125, and amemory 175. In exemplary embodiments, the exemplary LED array drivercircuit 100 also comprises one or more sensors 185, discussed in greaterdetail below.

The parallel array of LEDs 110 comprises a plurality of series-connectedLEDs, i.e., independent series or “strings” of LEDs, illustrated as “N”individual series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N). Eachsuch series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) may bereferred to equivalently herein as a “channel”, namely, channel one,channel two, channel three, through channel “N”, respectively. The“channel” connotation is particularly appropriate for the presentinvention which, as discussed in greater detail below, provides forindependently energizing each series of LEDs 110 ₁, 110 ₂, 110 ₃,through 110 _(N) using time-division modulation (“TDM”, or equivalently,time-division multiplexing).

Each series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) may haveeither the same or different types of LEDs. For purposes of explanationand understanding of the present invention, and without limitation as tothe scope of the invention, however, it may be assumed that each seriesof LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) have similarcharacteristics, such as by being fabricated by the same manufacturerand having only production or other manufacturing variations ortolerances. LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) having differentcharacteristics, such as be being produced from different manufacturers,may still be modeled appropriately, with corresponding informationstored in the memory 175, and with all such variations consideredequivalent and within the scope of the invention. As discussed ingreater detail below, various models of LED operation and devicecharacteristics are created and stored in memory 175, which may be anytype or form of memory, and which further may comprise a look up tablestructure or a database 180 structure, for example and withoutlimitation.

Each such channel may also comprise a corresponding bypass filtercapacitor 115 connected in parallel with each series of LEDs 110 ₁, 110₂, 110 ₃, through 110 _(N), illustrated as corresponding capacitors 115₁, 115 ₂, 115 ₃, through 115 _(N). The selection of the value of eachcorresponding capacitance, or the inclusion of any of the capacitors 115₁, 115 ₂, 115 ₃, through 115 _(N) altogether, is discussed in greaterdetail below.

The exemplary LED array driver circuit 100 further comprises a first,time-division or “energizing” multiplexer (or other array of powerswitches) 150, which provides for individually and selectively allowingcurrent to flow through each of the series of LEDs 110 ₁, 110 ₂, 110 ₃,through 110 _(N), i.e., turning on or off any selected series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N). Under the control of thecontroller 125, the multiplexer 150 is configured to allow currentthrough one or more of the series of LEDs 110 ₁, 110 ₂, 110 ₃, through110 _(N) in any combination, and for any selected duration (time periodor time slot), such as one series of LEDs 110, two series of LEDs 110,none of the series of LEDs 110, or all of the series of LEDs 110, forexample.

The illustrated exemplary power converter 120 comprises a DC voltagesource 105, a filter capacitor 135, an inductor 130, a switch 140, apeak current sense resistor (R1) 155, and the controller 125. The powerconverter 120 may be of any topology which is capable of or adapted todeliver a controlled current level to a load, such as a current having acontrolled peak to average current ratio, and may be isolated ornon-isolated, including a Buck, Boost, Buck-Boost, or Flybackconfiguration or topology. The DC voltage source 105 may be a batteryelement or an AC/DC converter (not separately illustrated), such as adiode bridge or rectifier, or a more complex, off line switching powersupply with power factor correction, for example. Also for example, theDC voltage source 105 also may be an AC/DC converter connected to phasemodulation AC device (typically wall dimmer) via an impedance matchingblock, not separately illustrated. The power converter 120 may operatein a continuous mode of operation (illustrated in FIG. 5) or adiscontinuous mode of operation (illustrated in FIG. 6).

The controller 125 may receive input from a wide variety of sources,including open or closed-loop feedback of various signals andmeasurements from within the LED array driver circuit 100, as discussedin greater detail below. Not separately illustrated, the controller 125may be coupled within a larger system, such as a computer-controlledlighting system in a building, and may interface with other computingelements using a wide variety of data transmission protocols, such asDMX 512, DALI, IC squared, etc.

The memory 175, which may include a data repository (or database) 180,may be embodied in any number of forms, including within any computer orother machine-readable data storage medium, memory device or otherstorage or communication device for storage or communication ofinformation, currently known or which becomes available in the future,including, but not limited to, a memory integrated circuit (“IC”), ormemory portion of an integrated circuit (such as the resident memorywithin a controller 125 or processor IC), whether volatile ornon-volatile, whether removable or non-removable, including withoutlimitation RAM, FLASH, DRAM, SDRAM, SRAM, MRAM, FeRAM, ROM, EPROM orE²PROM, or any other form of memory device, such as a magnetic harddrive, an optical drive, a magnetic disk or tape drive, a hard diskdrive, other machine-readable storage or memory media such as a floppydisk, a CDROM, a CD-RW, digital versatile disk (DVD) or other opticalmemory, or any other type of memory, storage medium, or data storageapparatus or circuit, which is known or which becomes known, dependingupon the selected embodiment. In addition, such computer readable mediaincludes any form of communication media which embodies computerreadable instructions, data structures, program modules or other data ina data signal or modulated signal, such as an electromagnetic or opticalcarrier wave or other transport mechanism, including any informationdelivery media, which may encode data or other information in a signal,wired or wirelessly, including electromagnetic, optical, acoustic, RF orinfrared signals, and so on. The memory 175 is adapted to store variouslook up tables, parameters, coefficients, other information and data,programs or instructions (of the software of the present invention), andother types of tables such as database tables, discussed below.

The controller 125 may be any type of controller or processor, and maybe embodied as one or more controllers 125, adapted to perform thefunctionality discussed below. As the term controller or processor isused herein, a controller 125 may include use of a single integratedcircuit (“IC”), or may include use of a plurality of integrated circuitsor other components connected, arranged or grouped together, such ascontrollers, microprocessors, digital signal processors (“DSPs”),parallel processors, multiple core processors, custom ICs, applicationspecific integrated circuits (“ASICs”), field programmable gate arrays(“FPGAs”), adaptive computing ICs, associated memory (such as RAM, DRAMand ROM), and other ICs and components. As a consequence, as usedherein, the term controller (or processor) should be understood toequivalently mean and include a single IC, or arrangement of custom ICs,ASICs, processors, microprocessors, controllers, FPGAs, adaptivecomputing ICs, or some other grouping of integrated circuits whichperform the functions discussed below, with associated memory, such asmicroprocessor memory or additional RAM, DRAM, SDRAM, SRAM, MRAM, ROM,FLASH, EPROM or E²PROM. A controller (or processor) (such as controller125), with its associated memory, may be adapted or configured (viaprogramming, FPGA interconnection, or hard-wiring) to perform themethodology of the invention, as discussed below. For example, themethodology may be programmed and stored, in a controller 125 with itsassociated memory (and/or memory 175) and other equivalent components,as a set of program instructions or other code (or equivalentconfiguration or other program) for subsequent execution when theprocessor is operative (i.e., powered on and functioning). Equivalently,when the controller 125 may implemented in whole or part as FPGAs,custom ICs and/or ASICs, the FPGAs, custom ICs or ASICs also may bedesigned, configured and/or hard-wired to implement the methodology ofthe invention. For example, the controller 125 may be implemented as anarrangement of controllers, microprocessors, DSPs and/or ASICs,collectively referred to as a “controller”, which are respectivelyprogrammed, designed, adapted or configured to implement the methodologyof the invention, in conjunction with a memory 175.

As indicated above, the controller 125 is programmed, using software anddata structures of the invention, for example, to perform themethodology of the present invention. As a consequence, the system andmethod of the present invention may be embodied as software whichprovides such programming or other instructions, such as a set ofinstructions and/or metadata embodied within a computer readable medium,discussed above. In addition, metadata may also be utilized to definethe various data structures of a look up table or a database 180. Suchsoftware may be in the form of source or object code, by way of exampleand without limitation. Source code further may be compiled into someform of instructions or object code (including assembly languageinstructions or configuration information). The software, source code ormetadata of the present invention may be embodied as any type of code,such as C, C++, SystemC, LISA, XML, Java, Brew, SQL and its variations(e.g., SQL 99 or proprietary versions of SQL), DB2, Oracle, or any othertype of programming language which performs the functionality discussedherein, including various hardware definition or hardware modelinglanguages (e.g., Verilog, VHDL, RTL) and resulting database files (e.g.,GDSII). As a consequence, a “construct”, “program construct”, “softwareconstruct” or “software”, as used equivalently herein, means and refersto any programming language, of any kind, with any syntax or signatures,which provides or can be interpreted to provide the associatedfunctionality or methodology specified (when instantiated or loaded intoa processor or computer and executed, including the controller 125, forexample).

The software, metadata, or other source code of the present inventionand any resulting bit file (object code, database, or look up table) maybe embodied within any tangible storage medium, such as any of thecomputer or other machine-readable data storage media, ascomputer-readable instructions, data structures, program modules orother data, such as discussed above with respect to the memory 175,e.g., a floppy disk, a CDROM, a CD-RW, a DVD, a magnetic hard drive, anoptical drive, or any other type of data storage apparatus or medium, asmentioned above.

FIG. 4 is a timing diagram for a first exemplary LED array drivercircuit 100, and illustrates the time division modulation for currentregulation in accordance with the teachings of the present invention. Asillustrated, each series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N)will be provided with a selected and independent current level, throughcontrol (by controller 125) of the switching state of each channel (viamultiplexer 150), for a selected time period (or duration), illustratedas first time period T_(Q1) for series of LEDs 110 ₁, second time periodT_(Q2) for series of LEDs 110 ₂, third time period T_(Q3) for series ofLEDs 110 ₃, fourth time period T_(Q4) for series of LEDs 110 ₄, through“N^(th)” time period T_(QN) for series of LEDs 110 _(N). The total timeperiod for providing current to all of the series of LEDs 110 ₁, 110 ₂,110 ₃, through 110 _(N) is referred to herein as “T_(C)”. Each of thesetime periods may be selected and varied during operation of the LEDarray driver circuit 100, providing time division modulation. Eachenergizing time period may be provided in any order or combination; forexample, series of LEDs 110 ₃ may be provided with current for thirdtime period T_(Q3), followed by series of LEDs 110 ₂ being provided withcurrent for second time period T_(Q4), followed by both series of LEDs110 ₁ and series of LEDs 110 _(N) being provided with selected currentlevels for corresponding first and N_(th) time periods T_(Q1) andT_(QN), respectively. In addition, the corresponding current levelsprovided during these time periods to each series of LEDs 110 ₁, 110 ₂,110 ₃, through 110 _(N) may be selected and varied during operation ofthe LED array driver circuit 100, as discussed in greater detail below,additionally providing for the average current regulation of the presentinvention. The intervals or time periods (illustrated as T_(A), T_(B),and T_(C)) between successive energizing time periods T_(Q1), T_(Q2)through T_(QN) may also be selected and varied, depending upon theselected embodiment.

Referring to the average DC current in each channel (series of LEDs 110₁, 110 ₂, 110 ₃, through 110 _(N)) as I_(Ci), (i.e., average DC currentI_(C1) for series of LEDs 110 ₁, average DC current I_(C2) for series ofLEDs 110 ₂, average DC current I_(C3) for series of LEDs 110 ₃, throughaverage DC current I_(CN) for series of LEDs 110 _(N)), then the averagecurrent I_(C) provided by the current source (in this case, powerconverter 120) is equal to

$I_{c} = {\sum\limits_{i = 1}^{i = n}{I_{ci}.}}$

With a period of time “T_(c)” to provide current (energize) all of theLED channels (all of the series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110_(N)), then the time of energizing each channel (series of LEDs 110)will be

$T_{Qi} = {\frac{I_{ci}T_{c}}{I_{c}}.}$

Referring to the switching cycle of power converter 120 as “T”, then

T_(Qi)=m_(i)T,

where m_(i) is the number of cycles of the power converter 120 perchannel (series of LEDs 110). In exemplary embodiments, although notrequired, the period of time T_(c) and the cycle time T is selected suchthat m_(i) is an interger.

EXAMPLE 1

For a system having three series of LEDs 110 ₁, 110 ₂, and 110 ₃, withaverage channel currents are initially set as I_(c1)=500 mA, I_(c2)=520mA, and I_(c3)=480 mA, then I_(c)500+520+480=1500 mA. AssumingT_(c)=1000 μs and T=1 μs, under the control of the controller 125directing switching through multiplexer 150, the power converter 120will supply to each channel a current of 150 mA for the run times

${T_{Q\; 1} = {\frac{500 \cdot 1000}{1500} = {333\mspace{14mu} {\mu s}}}},{T_{Q\; 2} = {\frac{520 \cdot 1000}{1500} = {347\mspace{14mu} {\mu s}}}},{and}$$T_{Q\; 3} = {\frac{480 \cdot 1000}{1500} = {320\mspace{14mu} {\mu s}}}$

which will result in the following number of cycles of the powerconverter 120: m₁=333, m₂=347, and m₃=320.

Continuing with the example, we may now suppose that for any of variousreasons, such as a,change in junction temperature, a change in coloroutput, etc., the current in channel one (series of LEDs 110 ₁) only isto be adjusted to 275 mA, while the previous current levels are to bemaintained in the remaining channels 2 and 3 (series of LEDs 110 ₂ andseries of LEDs 110 ₃). Accordingly, the total average DC current to beprovided by the power converter 120 is now I_(c)=275+520+480=1275 mA,resulting in:

${T_{Q\; 1} = {\frac{275 \cdot 1000}{1275} = {216\mspace{14mu} {\mu s}}}},{T_{Q\; 2} = {\frac{520 \cdot 1000}{1275} = {408\mspace{14mu} {\mu s}}}},{and}$${T_{Q\; 3} = {\frac{480 \cdot 1000}{1275} = {376\mspace{14mu} {\mu s}}}},{{{with}\mspace{14mu} m_{1}} = 216},{m_{2} = 408},{{{and}\mspace{14mu} m_{3}} = 376.}$

An exemplary boost converter may be utilized to generate the requiredaverage current I_(c) in every channel. In addition to those illustratedbelow in the Examples, those skilled in the art may derive similarequations for other power converter (or current source) topologies.

EXAMPLE 2

For a continuous conduction mode (“CCM”), as illustrated in FIG. 5,

${I_{c} = {\frac{I_{p\; 1i} + I_{p\; 2i}}{2} \cdot \frac{t_{r\; 1}}{T}}},$

where

I_(p1i)—First peak current, Channel i;

I_(p2i)—Second peak current, Channel i; and

t_(ri)—reset time, Channel i.

Two variables are introduced for ease of explanation and derivation ofequations, as follows:

${a_{i} = \frac{I_{p\; 2i}}{I_{p\; 1i}}},$

namely, the ratio of the second peak current to the first peak currentfor a selected ith channel, and

${b_{i} = \frac{t_{ri}}{T}},$

namely, the ratio of the switch 140 reset time (i.e., off or open time)to the total cycle time, resulting in a first peak current for an ithchannel of:

$I_{p\; 1i} = {\frac{2I_{c}}{\left( {1 + {ai}} \right)b_{i}}.}$

Another expression for the first peak current I_(p1i) is:

$I_{p\; 1i} = {I_{p\; 2i} + \frac{V_{i\; n} \cdot t_{oni}}{L}}$

where

V_(in)—Input voltage from DC voltage source 105;

t_(oni)—on time, Channel i; and

L—inductance value of inductor 130.

With substitutions

$I_{p\; 1i} = \frac{V_{in} \cdot t_{oni}}{\left( {1 - a_{i}} \right)L}$

then one more expression for I_(p1i) current is

$I_{p\; 1i} = {I_{p\; 2i} + \frac{\left( {V_{outi} - V_{in}} \right) \cdot t_{ri}}{L}}$

where

V_(outi)—output voltage, ith channel;

or

$I_{p\; 1i} = {\frac{\left( {V_{oui} - V_{in}} \right) \cdot t_{ri}}{\left( {1 - a_{i}} \right)L}.}$

From FIG. 5, for the continuous mode, we also have T=t_(oni)+t_(ri), andthe cycle time T is the same for all channels. Solving the above systemof equations provides:

$b_{i} = \frac{V_{in}}{V_{oui}}$

and

$a_{i} = \frac{{2{I_{c} \cdot L}} - {\left( {V_{outi} - V_{in}} \right)b_{i}^{2}T}}{{2I_{c}L} + {\left( {V_{outi} - V_{in}} \right)b_{i}^{2}T}}$

As will be apparent from the derivation above, constant values may beknown or selected for the inductance L of inductor 130, the cycle time Tfor the power converter 120, and the average DC current I_(c), withcorresponding values stored in memory 175. Using coefficients a_(i) andb_(i), as an example, allows the computation (by controller 125) of thevalues of the first and second peak currents per channel, I_(p1i) andI_(p2i), for operation of the power converter 120, provided the inputand output voltages are known. Input voltage V_(in) (from DC voltagesource 105) can be measured (e.g., through a sensor 185), selected orotherwise predetermined, with a value stored in memory 175. Initially,however, the output voltage V_(outi) across an individual series of LEDs110 cannot be measured, because the computations occur before the powerconverter 120 provides current to the series of LEDs 110. In accordancewith the present invention, therefore, the output voltage for a channelV_(outi) is initially predicted by employing digital models of the LEDs110, with such models (as parameters) stored in memory 175 and utilizedby the controller 125. Knowing the DC current through a selected seriesof LEDs 110, I_(ci), and using device specifications, data sheets, orother data provided by the LED device manufacturer, the output voltage(i.e., voltage drop) across each of the series of LEDs 110, as functionof forward current, may be determined and provided in the form of a lookup table stored in memory 175, in graphical form, or any in other formknown to those skilled in the digital electronics design arts.

This more theoretical prediction, however, may have an error component,due to manufacturing tolerances, age, junction temperature relateddrift, or any other physical parameter or variable of LED performance,leading to a forward voltage change. In accordance with the exemplaryembodiments of the present invention, the actual output voltage acrosseach series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) is measured,also using a sensor 185. Corresponding to such measurements,compensation coefficients are introduced, stored in memory 175, andutilized for subsequent output voltage prediction by the controller 125,for use in successive iterations (i.e. successive time periods “T_(C)”),as discussed above. These compensation coefficients can be saved andstored for each channel, and may be updated periodically (comparativelyinfrequently), as they are associated with LED 110 device parameterswhich change comparatively slowly.

EXAMPLE 3

For a discontinuous conduction mode (“DCM”), as illustrated in FIG. 6,peak current I_(p1i) is defined as

$I_{p\; 1i} = \frac{2I_{c}T}{t_{ri}}$

Also, for a boost configuration using DCM:

$I_{p\; 1i} = \frac{V_{in} \cdot t_{oni}}{L}$

and volt-seconds balance across inductor 130 is:

V _(in) ·t _(oni)=(V _(outi) −V _(in))·t _(ri)

The peak current I_(p1i) is then:

$I_{p\; 1i} = \frac{2{I_{c} \cdot V_{outi}}}{V_{in}}$

The technique of generating the value of the output voltage V_(outi) isthe same as described above for CCM of operation. The boundary betweenCCM and DCM may be found analytically by solving the following equation,or by determining if the actual cycle time, after current discharge bythe inductor 130 is completed, is equal to the set cycle time T:

$T = \frac{2I_{c}{LV}_{outi}^{2}}{V_{in}^{2}\left( {V_{oui} - V_{in}} \right)}$

The amplitude of voltage ripple ΔV_(i) in a selected channel i is givenby the following relationship, from which the capacitance values ofcapacitors 115 may be determined:

${\Delta \; V_{i}} = \frac{I_{c} \cdot T_{Qi}^{2}}{C_{i} \cdot T_{c}}$

Referring again to FIG. 3, the controller 125 receives one or moreinputs from any of various sources, such as from one or more sensors185, or from other systems, such as a master lighting controller orcontrol system (not separately illustrated), using any type ofcommunication protocol, such as accommodating a standard interfacebetween digital controllers such as DMX512, DALI, IC squared, radiofrequency, Ethernet and many other communication protocols and/orinterfaces, as known or becomes known in the art.

The various sensors 185 may be analog and/or digital, and will becoupled to corresponding input ports of the controller 125. For example,an analog peak current may be measured (e.g., across resistor 155, whichfunctions as a peak current sensor), and converted (utilizing an analogto digital converter, not separately illustrated), to provide a digitalvalue of peak current for storage in memory 175. Such a measured peakcurrent value may be compared within controller 125, such as through acomparator (not separately illustrated), with corresponding controlprovided by the controller 125 to the DC voltage source 105 and/orswitch 140 to adjust peak current levels. As indicated above, LEDmodels, other parameters, specifications, coefficients, etc., are storedin digital form in memory 175. The controller 125 also generallyincludes buffer (or other driver) circuits to provide the switchingcontrol for the multiplexer (or other power switches) 150 and theswitching (of switch 140) of the exemplary LED array driver circuit 100.

The various sensors 185 providing input to analog and/or digital portsof the controller 125 generate sense signals from each channel, theexemplary LED array driver circuit 100 environment, and potentially thelarger lighting system environment. Exemplary sensors 185, for exampleand without limitation, may be sensors for: electrical (output voltage,string current), optical (brightness, wavelengths emission, colortemperature, chromaticity, radiant power, luminous power in ), thermal(junction temperature, ambient temperature), environmental (ambientlighting), mechanical (displacement, angular, strain, velocity,acceleration), magnetic, hall sensors, and more specific sensorsproviding signals related to the functional purposes of the system(e.g., residential illumination, architectural, signage, automotivelighting, backlighting, emergency lighting, naval lighting and others).

In exemplary embodiments, the controller 125 receives input controlsignals and feedback (or sensed) signals to generate the average DCcurrents to be set for each channel I_(ci) and the duty cycle for thetime-division modulation average current control of the exemplary LEDarray driver circuit 100 in accordance with the present invention. Forexample, in and exemplary embodiment, DC currents I_(ci) for eachchannel may be determined by control signals coming from an overallsystem controller, such as based upon the type or manufacture of LEDsused in the LED array 110 (series of LEDs 110 ₁, 110 ₂, 110 ₃, through110 _(N)) In another exemplary embodiment, DC currents I_(ci) for eachchannel may be determined as a result of specific algorithms, with thecontroller 125 processing LED feedback (or sensed) information andadjusting the amplitude of average currents I_(ci) to compensate forunwanted changes and age drift of the LED system in any area ofelectrical, optical, thermal and functional performance. The controller125 also utilizes the digital models of electrical behavior for eachstring of LEDs (series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N)) bysupplying forward current using the models and determining errorcoefficients for each model by comparing the actual output voltagesacross each series of LEDs 110 (measured and fed back) with thepredicted output voltages, as discussed above.

The controller 125 is also the functional controller of the converter120, selecting the cycle time “T” of the converter 120 and determiningthe peak current for each channel I_(p1i), based on its input signals,discussed above. The controller 125 also synchronizes this set value ofthe peak current with one of the active LED channels (series of LEDs110), computes the energizing time periods or durations (on times or runtimes) of the channels, T_(Qi), and controls the status of themultiplexer 150 switching according to these required energizing timeperiods (on times or run times) T_(Qi), synchronizing such switchingwith the corresponding set values of I_(p1is) for each series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N).

FIG. 7 is a circuit and block diagram illustrating a second exemplaryLED array driver circuit 200, implemented as a boost-type converter, inaccordance with the teachings of the present invention. The secondexemplary LED array driver circuit 200 comprises a (switching) powerconverter 220, a parallel array of LEDs 110 (series of LEDs 110 ₁, 110₂, 110 ₃, through 110 _(N)) with corresponding bypass filter capacitors115 and voltage dividers 230 (discussed below), a first, time-divisionmultiplexer (or other array of power switches) 150, a second, currentsense multiplexer 250, a third, voltage sense multiplexer 210, acontroller 225, a memory 175, and a plurality of resistors 265 in serieswith each channel (illustrated as corresponding resistors 265 ₁, 265 ₂,265 ₃, through 265 _(N). In exemplary embodiments, the second exemplaryLED array driver circuit 200 one or more of the sensors 185 areimplemented, for example, utilizing voltage divider 240 and voltagedividers 230 ₁, 230 ₂, 230 ₃, through 230 _(N).

In addition to the features previously discussed for power converter120, the power converter 220 further comprises a voltage divider 240, a(total) current sense resistor 255, and corresponding blocking(Schottky) diodes 145 (for each series of LEDs 110 ₁, 110 ₂, 110 ₃,through 110 _(N)). In addition, the switch 140 is implemented as aMOSFET 140 ₁, having its drain connected to inductor 130 and its sourceconnected to the current sense resistor 255.

The parallel array of LEDs 110 also comprises a plurality ofseries-connected LEDs, i.e., independent series or “strings” of LEDs,illustrated as “N” individual series of LEDs 110 ₁, 110 ₂, 110 ₃,through 110 _(N), as previously discussed. Each such channel may alsocomprise a corresponding bypass filter capacitor 115 connected inparallel with each series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N),illustrated as corresponding capacitors 115 ₁, 115 ₂, 115 ₃, through 115_(N), as previously discussed. Each such channel also comprises acorresponding voltage divider 230 also connected in parallel with eachseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), illustrated ascorresponding voltage dividers 230 ₁, 230 ₂, 230 ₃, through 230 _(N). Aplurality of corresponding output current sense resistors (265 ₁, 265 ₂,265 ₃, through 265 _(N)) are also utilized, as illustrated.

The controller 225 has all of the functionality of the controller 125previously discussed, plus the additional functionality discussed below.In addition to the time-division multiplexer (or other array of powerswitches) 150 and switch 140, the voltage sense multiplexer 210 andcurrent sense multiplexer 250 are also under the control of thecontroller 225. As discussed above, the exemplary LED array drivercircuit 200 further comprises a first, time-division or “energizing”multiplexer (or other array of power switches) 150, which provides forindividually and selectively allowing current to flow through each ofthe series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), i.e., turningon or off any selected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110_(N). Under the control of the controller 225, when the time divisionmultiplexer 150 is switched to a selected LED series 110 (of theplurality of series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N)) forallowing current to flow through that selected LED series 110 for aselected period of time (T_(QN)), the voltage sense multiplexer 210 andcurrent sense multiplexer 250 are concurrently switched forcorresponding sensing of the voltage and current levels for the sameselected LED series 110, as follows: (1) the voltage sense multiplexer210 is concurrently switched to the voltage divider 230 which is coupledin parallel to the same selected LED series 110, for output voltagedetection (sensing) for that selected channel; and (2) the current sensemultiplexer 250 is also switched to the same selected LED series 110 fordetection (sensing) of the current flowing through the selected LEDseries 110.

Functional blocks of the controller 225 are also illustrated in FIG. 7,including one or more analog-to-digital (A/D) converters 205, one ormore comparators 215, control logic 235, and switching buffers (ordrivers) 245 (for controlling the switching of the various multiplexers150, 210, 250 for the time-division modulation of the present invention.As illustrated, corresponding voltages, representing: (1) input voltage(from voltage divider 240), (2) an output voltage across a selectedseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) (from thecorresponding voltage divider 230) selected via voltage sensemultiplexer 210, (3) peak current (from current sense resistor 255), and(4) output current through a selected series of LEDs 110 ₁, 110 ₂, 110₃, through 110 _(N) (across output current sense resistors (265 ₁, 265₂, 265 ₃, through 265 _(N)) selected via current sense multiplexer 250),are provided to corresponding A/D converters 205, and are thencorrespondingly compared in comparators 215, with the correspondingresults provided to control logic 235, for use in determining thecurrent to be provided to each channel (driving the various multiplexers150, 210 and 250 via switching buffers 245) for the corresponding timeduration (T_(QN)) for the time-division modulation of the presentinvention, as discussed above. Not separately illustrated, thecontroller 225 may also include an oscillator (for clocking the variouscomponents) and a voltage regulator.

In this exemplary LED array driver circuit 200, using correspondingcomparators 215 and control logic 235: (1) actual peak current (fromcurrent sense resistor 255) may be compared to the set or predeterminedpeak current (from an input or stored in memory 175), and ifsufficiently different, adjusted accordingly; (2) actual output currentthrough a selected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N)(across output current sense resistors (265 ₁, 265 ₂, 265 ₃, through 265_(N)) may be compared to the corresponding set or predetermined outputcurrent (from an input or stored in memory 175), and if sufficientlydifferent, adjusted accordingly; (3) input voltage (from voltage divider240) may be compared to the set or predetermined input voltage level(from an input or stored in memory 175), and if sufficiently different,adjusted accordingly; and (4) an output voltage across a selected seriesof LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) (from the correspondingvoltage divider 230) may be compared to the corresponding set orpredetermined output voltage level (from an input or stored in memory175), and if sufficiently different, adjusted accordingly.

The exemplary LED array driver circuit 200 is implemented based on thefollowing hysteretic process of time-division modulation, consisting ofthe following steps, implemented in the controller 225 and the otherspecified components:

(1) Setting values of DC currents in each channel, based on inputsignal.

(2) Calculating the source DC current I_(c) as substantially or aboutequal to sum of each channel DC current I_(ci):

$I_{c} = {\sum\limits_{i = 1}^{i = n}\; {I_{ci}.}}$

(3) Monitoring current in the inductor 130 of the power converter 220and when this current is equal to zero, sequentially turning on thepower switch of a selected series of LEDs 110 ₁, 110 ₂, 110 ₃, through110 _(N) (the “active” string) via the time-division multiplexer 150,while keeping the rest of the power switches in an off state, also viathe time-division multiplexer 150.

(4) Correspondingly and synchronously turning on the switches withinvoltage sense multiplexer 210 and current sense multiplexer 250,corresponding to the active string LEDs 110 (the selected series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N)), for the correspondingtime-division modulation periods or durations.

(5) Monitoring the DC current level in the active string, and (a) if thecurrent is higher than the corresponding predetermined or set value,deactivate the current series of LEDs 110 and activating the next seriesof LEDs 110 in the sequence; or (b) if the DC current level is less thanthe corresponding predetermined or set value, continuing the process ofenergizing the selected active series of LEDs 110.

(6) Measuring the operating input DC Voltage (across voltage divider240).

(7) Measuring operating output voltage of the selected, active series ofLEDs 110, (across a corresponding voltage divider 230).

(8) Calculating peak current of the power converter 220 according to

$I_{p\; 1i} = {\frac{2{I_{c} \cdot V_{outi}}}{V_{in}}.}$

(9) Alternatively the last three steps (6, 7 and 8 above) can beimplemented by measuring the reset time t_(ri); measuring actual cycletime T; and calculating the peak current of the converter 220 as

$I_{p\; 1i} = {\frac{2I_{c}T}{t_{r}}.}$

(10) Running converter 220 in constant peak current mode in the DCM modewith preselected constant cycle time and peak current value calculatedseparately for each string.

(11) Monitoring DC current in the active, selected series of LEDs 110 ₁,110 ₂, 110 ₃, through 110 _(N): when DC current reaches thecorresponding predetermined or set value, terminating the switchingcycle of the converter 220, and if the switch 140 ₁ is currently in anoff state, waiting until current in the inductor 130 drops to about zerobefore starting the process of energizing of the next selected series ofLEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N); or if the switch 140 ₁ iscurrently in an on state, turning the switch 140 ₁ off (e.g.,immediately) and then waiting until current in the inductor 130 drops toabout zero before starting the process of energizing of the nextselected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N).

(12) At the end of sequence of energizing each of the series of LEDs 110₁, 110 ₂, 110 ₃, through 110 _(N), updating all parameters of theoperation and driving of the exemplary LED array driver circuit 200 foreach channel, and starting the next driving cycle of the exemplary LEDarray driver circuit 200.

The required DC current level of each series of LEDs 110 ₁, 110 ₂, 110₃, through 110 _(N) is supplied as input to control logic 235. Thecontrol logic 235 calculates the total equivalent DC current of theconverter 220 for the total period T which will include a sequentialactivation of all series of LEDs 110. The peak current is adjusted foreach series of LEDs 110 by measuring input voltage via voltage divider240 and one of the A/D converters 205. Output voltage of the active,selected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) is sensedby the corresponding voltage divider 230, selected via voltage sensemultiplexer 210 and input to one of the A/D converters 205. Theselection by the voltage sense multiplexer 210 is synchronized with thetime division multiplexer 150, so only active series of LEDs 110 (powerswitch is on) is selected for voltage sensing. The switch 140 ₁ of theboost converter 220 is controlled by the switching buffers 245, based ondeterminations by the control logic 235, comparing the sensed peakcurrent across resistor 255 with the predetermined or set value for eachseries of LEDs 110. The set value of peak current may be different foreach series of LEDs 110, depending on its DC voltage and is determinedby comparisons performed by control logic 235. Via switching buffers245, the control logic 235 controls the switching status, switchingselections, and switching synchronization of the time divisionmultiplexer 150, the current sense multiplexer 250, and the voltagesense multiplexer 210, such that only the active series of LEDs 110 issensed.

In this embodiment, the time periods for each of the series of LEDs 110for the time division modulation is not required to be analyticallydetermined. Because the DC current supplied by a boost converter 220 ismuch higher that any required DC current of the selected series of LEDs110, the actual DC current in the active series of LEDs 110 will alwaysbe ramping up. Based on the monitored DC current in the active series ofLEDs 110, when comparator 215 and/or control logic 235 identifies thatthe DC current in the active series of LEDs 110 is equal to thepredetermined or set current value for the selected series of LEDs 110,that selected series of LEDs 110 will be deactivated. For example,threshold levels of the comparator 215 may be set to a unique value foreach series of LEDs 110.

Additional configurations for switching and sensing, for the exemplaryLED array driver circuits 100, 200 are illustrated in FIGS. 8, 9, 11 and12. FIG. 8 is a circuit 300 diagram illustrating high side driving(301), as an exemplary switching implementation of a time-divisionmultiplexer 150 ₁, with low side sensing (302), for a series of LEDs 110_(N) in accordance with the teachings of the present invention. FIG. 9is a circuit diagram illustrating differential high side sensing (303)and low side driving (304), as an exemplary switching implementation ofa time-division multiplexer 150 ₂, for a series of LEDs 110 _(N) inaccordance with the teachings of the present invention. As illustrated,the switching through the time division multiplexer 150 may be providedon either the high (150 ₁) or low (150 ₂) sides of each series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N). High side switching (FIG. 8) maybe slightly more expensive and slower than low side switching, but mayprovide greater accuracy. Accordingly, if the speed of systemperformance over its accuracy is more important, then high side sensingand low side switching may be selected. Those of skill in the art willrecognize that different combinations of low and high side switching(drivers) and sensing circuits may be utilized to achieve the bestperformance of an LED array driver circuit 100, 200

FIG. 10 is a graphical diagram illustrating simulation of a boost LEDarray driver circuit, for three series of LEDs, in accordance with theteachings of the present invention. FIG. 10 is illustrated for a Vin of5 V, a filter 115 capacitance of 2.2 μF, a first series of three LEDs(LEDs₁) having a current setting of 50 mA, a second series of four LEDs(LEDs₂) having a current setting of 40 mA, and a third series of fiveLEDs (LEDs₃) having a current setting of 30 mA, with dimming to 50% at100 μs and returning back to 100% after 240 μs. DC current ripple may beadjusted by a selection of appropriate values of filter capacitors 115.In turn, this selection depends on the switching frequency of the switch140, 140 ₁ and the cycle time of time division multiplexer 150, with ahigher switching frequency and smaller cycle time T_(c) enabling asmaller filter 115 capacitance to achieve the same ripple current. Asillustrated in FIG. 10, time division modulation creates a relativelypoor response, based on the time required to discharge or charge filtercapacitors 115. If duty cycle of switching (of switch 140, 140 ₁) issmall and cycle time T_(c) is small, that may considerably affect theresponse of the system to the required accuracy and speed of change oflighting intensity, color temperature adjustments, or creating coloreffects.

FIGS. 11 and 12 are circuit diagrams illustrating a first circuit 310configuration and a second circuit 330 configuration, respectively, ofan LED array for independent time division modulation. FIG. 13 is agraphical diagram illustrating simulation of LED current in a boost LEDarray driver circuit, for three LED strings implemented according to theconfiguration of circuit 310 of FIG. 11, with simultaneous switching asillustrated for a first series of three LEDs (LEDs₁) having a currentsetting of 50 mA, a second series of four LEDs (LEDs₂) having a currentsetting of 40 mA, and a third series of five LEDs (LEDs₃) having acurrent setting of 30 mA.

As illustrated in FIG. 11, the time division multiplexer 150 isimplemented in a distributed manner, as the illustrated time divisionmultiplexer 150 ₃ having corresponding switches on both the high and lowsides of each series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N). Asillustrated in FIG. 12, the time division multiplexer 150 is alsoimplemented in a distributed manner, as the illustrated time divisionmultiplexer 150 ₄ having corresponding switches on the high side of eachseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) and one switch onthe low side of filter capacitors 115.

Also as illustrated in FIG. 11, the configuration of circuit 310provides for fast switching speeds for the time division modulation,allowing independent time division modulation for each series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N) by substantially simultaneouslyturning on/off corresponding pairs of switches 315 _(2A) and 315 _(B) ofthe time division multiplexer 150 ₃ for each series of LEDs 110 ₁, 110₂, 110 ₃, through 110 _(N), illustrated as corresponding switching pairs315 _(1A) and 315 _(1B), 315 _(2A) and 315 _(2B), through 315 _(NA) and315 _(NB). The edges of current pulses through the LEDs 110 may be veryfast, on the order of tens to hundreds of nanoseconds, unlessspecifically slowed down to curtail electromagnetic interference (EMI).The switches 315 _(1A) and 315 _(1B), through 315 _(NA) and 315 _(NB),may be unidirectional (like MOSFETs with body diode conducting whencapacitors 115 are being charged). For less power dissipation a Schottkydiode 329 may be connected in parallel with the MOSFET body diode.

When individual time division modulation of each series of LEDs 110 ₁,110 ₂, 110 ₃, through 110 _(N) is not required, such as for energizingone or more of the series of LEDs at substantially the same time, suchas in various groups, the time division multiplexer 150 may besimplified by having a corresponding plurality of high side switches 315_(A) and only one low side switch 315 _(B) comprising time divisionmultiplexer 150 ₄, as illustrated in FIG. 12. This configuration ofcircuit 330 operates similarly to circuit 310, except for simultaneousconnection or disconnection of filter capacitors 115 from series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N). The current in the series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N) is completely disabled when allswitches 315 are turned off synchronously. To enable current flow in aselected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), theswitch 315 _(B) and one of the switches 315 _(1A), 315 _(2A), through315 _(NA) (corresponding to the selected series of LEDs 110) are turnedon.

Continuing to refer to FIGS. 11 and 12, each series, or any selectedseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), may be separatelyand independently energized as follows, for each such series of LEDs110: (1) establish DC current in each series of LEDs 110 by DC currentregulation, keeping the one of the switches 315 _(1A), 315 _(2A),through 315 _(NA) of the time division multiplexer 150 ₃ or timedivision multiplexer 150 ₄ in an on or off state as required to regulatethe DC level of the current through the selected series of LEDs 110 ₁,110 ₂, 110 ₃, through 110 _(N), and keeping one of the correspondingfilter capacitor switches 315 _(1B), 315 _(2B), through 315 _(NB) in acorresponding on or off state (or keeping the single switch 315 _(B) inan on state continuously); (2) determining the corresponding time period(or duty ratio) for time-division modulation for each series of LEDs 110₁, 110 ₂, 110 ₃, through 110 _(N) (a duty ratio 100% will mean thatstring is permanently on DC current regulation); (3) for each series ofLEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), monitoring elapsed timeand/or counting the number of cycles “m” of the switching of the powerconverter, and when either is substantially equal to the correspondingpredetermined or set value, monitoring the current in inductor 130 ofthe converter, and when the inductor 130 current is substantially zero,turning off the corresponding switch 315 _(1A), 315 _(2A), through 315_(NA) of the time division multiplexer 150 ₃ or time divisionmultiplexer 150 ₄ and turning off the corresponding filter capacitorswitches 315 _(1B), 315 _(2B), through 315 _(NB) or turning off thesingle switch 315 _(B) of a series of LEDs 110 to be disabled; (4)optionally determining the converter peak current I_(p1i) based onsource current I_(c) and parameters of the active series of LEDs 110;and (5) at the end of the particular switching cycle of the converter,turning on the next one of the switches 315 _(1A), 315 _(2A), through315 _(NA) and corresponding filter capacitor switches 315 _(1B), 315_(2B), through 315 _(NB) (or the single switch 315 _(B)) to energize thenext selected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N).

FIG. 14 is a flow diagram illustrating an exemplary method oftime-division modulation for separately and independently energizing aselected series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) inaccordance with the teachings of the present invention, and provides auseful summary of exemplary features of the present invention. Themethod begins, start step 400, with determining corresponding values orlevels of a DC current for each series (or channel) of LEDs 110 ₁, 110₂, 110 ₃, through 110 _(N), step 405. The method calculates the sourceDC current I_(c), to be provided by the converter 120, 220, step 410, assubstantially or about equal to the sum of each channel DC currentI_(ci), namely,

$I_{c} = {\sum\limits_{i = 1}^{i = n}\; {I_{ci}.}}$

A total period “T” is determined for switching current to all of theseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), and acorresponding time period for energizing each selected series of LEDs110 ₁, 110 ₂, 110 ₃, through 110 _(N) is determined, step 415, assubstantially equal to a proportion of the total period (for switchingcurrent to all of the series of light-emitting diodes of the pluralityof series of light-emitting diodes), determined as a ratio of thecorresponding current for the selected corresponding series oflight-emitting diodes to the total (average) current provided by thepower converter, namely,

$T_{Qi} = {\frac{I_{ci}T_{c}}{I_{c}}.}$

The operating mode of the converter is selected, namely, whetheroperating in continuous or discontinuous current mode, and a switchingfrequency of the power converter 120, 220 may also be selected (based onwhether the power converter 120, 220 is to be operated in discontinuousor continuous current mode), step 420. Those of skill in the art willappreciate that steps 405, 410, 415 and 420 may occur in any order orconcurrently, and also may be performed in advance of the operation ofthe system or apparatus.

Continuing to refer to FIG. 14, during operation of the system orapparatus, step 425, the operating input DC voltage of the converter120, 220 is measured, such as across a voltage divider 240. In step 430,the output DC voltage for each series of LEDs 110 is predictedinitially, such as by using various models or device parameters, and isthen updated subsequently (using the error coefficients) based onmeasurements of the corresponding output voltage across the selectedseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N), typicallydetermined as a corresponding voltage across a voltage divider 230. Afirst peak current is also calculated for CCM or a peak current for DCM,step 435. Those of skill in the art will also appreciate that theprediction step 430, and determination step 435 may occur in any orderor concurrently, and also may be performed in advance of the operationof the system or apparatus (for an initial prediction).

As previously mentioned, the prediction of the output voltage acrosseach series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) is typicallybased on device parameters, such as a manufacturer's specification of aforward voltage drop as function of a forward current of LED and thenumber of LEDs in series, for a selected series of LEDs 110 ₁, 110 ₂,110 ₃, through 110 _(N). The output voltage of each selected series ofLEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) is also measured periodicallyto determine and/or update an error coefficient, such that the outputvoltage prediction is updated based on multiplying the predicted valueby the error coefficient, for a more accurate output voltage prediction.This comparison of the predicted and measured voltages allowscompensation for any effects of manufacturing production variations andtolerances, LED junction temperature variations, age drift and otherfactors, any and all of which can contribute to changes of theelectrical characteristics of LEDs 110.

The power converter 120, 220 is then operated with the constant peakcurrent, constant cycle time and constant DC current I_(c), step 440,and with driving each selected series of LEDs 110 ₁, 110 ₂, 110 ₃,through 110 _(N) for the corresponding time-division T_(Qi) time periodor until the corresponding predetermined current level is reached, step445, by switching each selected series of LEDs 110 ₁, 110 ₂, 110 ₃,through 110 _(N) on and off, i.e., coupling to and uncoupling from theoutput of power converter 120, 220, generally at times when the powerconverter 120, 220 is building current in the inductor 130 and notsupplying current to the output load (i.e., when the inductor 130current is substantially zero). When monitoring of corresponding currentlevels is utilized in step 445 to implement the time-divisionmultiplexing of the present invention, those having skill in the artwill recognize that all or part of step 415 may be omitted from themethodology. Following each energizing of a selected series of LEDs 110₁, 110 ₂, 110 ₃, through 110 _(N), or following the energizing of all ofthe s series of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) (e.g., at theend of a period “T”), all parameters of power converter 120, 220operation and driving parameters for each series of LEDs 110 ₁, 110 ₂,110 ₃, through 110 _(N) are updated (e.g., such as for use in predictingcorresponding output voltages), step 450. When the energizing of theseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) is to be continued,step 455, the method returns to step 405 and iterates, and otherwise themethod may end, returns step 460.

The apparatus, system and method of driving a single or plurality ofseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) may be used forcontrolling the performance of an LED system, for example, controllingbrightness, color temperature, color control or dimming. Anothersignificant and effective use of this method comprises localcompensation of the drift of LED parameters due to junction temperaturechanges, age, manufacturing variations and tolerances, and othercharacteristics and parameters.

Another variation of the above time-division modulation may also beimplemented. Rather than changing a duty ratio of each switching cycleof a power converter 120, 220, as is done with pulse-width modulation,the time-division modulation may also be implemented in DCM by skippingcycles of the power converter 120, 220, i.e., by shutting down the powerconverter 120, 220 for a predetermined number of cycles. For example,the number of cycles to be skipped is calculated, based on a full numberof cycles m_(i) and the required time periods T_(QN) of thetime-division modulation. The power converter 120, 220 is run indiscontinuous current mode, with time-division modulation implemented byshutting down the power converter 120, 220 for a complete number ofskipped cycles during one total period “T”. In this embodiment, thereare fewer switching events than a driver with standard PWM, thusreducing EMI and simplifying power converter 120, 220 design forcontrolling EMI.

The above description of the power converter 120, 220 and regulator isexemplary. Those skilled in the art will recognize that any topology ofpower converter 120, 220 may be utilized, such as buck, buck boost, orflyback. A direct conversion of AC input into a controlled currentsource may also be achieved by different AC/DC topologies. Any number ofseries of LEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N) may be implemented,using a corresponding number of switches and/or multiplexers. Also, ifthe actual output voltage across each of the series of LEDs 110 ₁, 110₂, 110 ₃, through 110 _(N) is expected to be the same, the outputvoltage may be measured for one selected series, rather than all, ofLEDs 110 ₁, 110 ₂, 110 ₃, through 110 _(N).

Numerous advantages of the present invention are readily apparent. Thevarious embodiments of the invention provide innumerable advantages forenergizing a plurality of series (strings) of LEDs, using a single powerconverter and controller for an entire LED array, and does not utilizemultiple, separate power converters and controllers for each LED string.The exemplary embodiments provide a multistring LED driver whichcontrols current independently for each series of LEDs of the array, forcorresponding effective color and brightness control, among otherfeatures, throughout the life span of the LEDs and corresponding changesin their functional parameters. In addition, the exemplary LED arraydrivers provide for local, faster and comprehensive LED regulation,providing local compensation of LED emission due to age and drift ofsuch functional parameters, temperature changes of the LED junction, LEDproduction characteristics variation, and variations of devices producedby different manufacturers. The exemplary LED array drivers are alsobackwards-compatible with legacy LED control systems, frees the legacyhost computer for other tasks and allows such host computers to beutilized for other types of system regulation.

Although the invention has been described with respect to specificembodiments thereof, these embodiments are merely illustrative and notrestrictive of the invention. In the description herein, numerousspecific details are provided, such as examples of electronic andelectrical components, materials, and structural variations, to providea thorough understanding of embodiments of the present invention. Oneskilled in the relevant art will recognize, however, that an embodimentof the invention can be practiced without one or more of the specificdetails, or with other apparatus, systems, assemblies, components,materials, parts, etc. In other instances, well-known structures,materials, or operations are not specifically shown or described indetail to avoid obscuring aspects of embodiments of the presentinvention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or a specific “embodiment” means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention and notnecessarily in all embodiments, and further, are not necessarilyreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics of any specific embodiment of the presentinvention may be combined in any suitable manner and in any suitablecombination with one or more other embodiments, including the use ofselected features without corresponding use of other features. Inaddition, many modifications may be made to adapt a particularapplication, situation or material to the essential scope and spirit ofthe present invention. It is to be understood that other variations andmodifications of the embodiments of the present invention described andillustrated herein are possible in light of the teachings herein and areto be considered part of the spirit and scope of the present invention.

It will also be appreciated that one or more of the elements depicted inthe Figures can also be implemented in a more separate or integratedmanner, or even removed or rendered inoperable in certain cases, as maybe useful in accordance with a particular application. Integrally formedcombinations of components are also within the scope of the invention,particularly for embodiments in which a separation or combination ofdiscrete components is unclear or indiscernible. In addition, use of theterm “coupled” herein, including in its various forms such as couplingor couplable, means and includes any direct or indirect structural,electrical or magnetic coupling, connection or attachment, or adaptationor capability for such a direct or indirect structural, electrical ormagnetic coupling, connection or attachment, including integrally formedcomponents and components which are coupled via or through anothercomponent. Furthermore, the disjunctive term “or”, as used herein andthroughout the claims that follow, is generally intended to mean“and/or”, having both conjunctive and disjunctive meanings (and is notconfined to an “exclusive or” meaning), unless otherwise indicated. Asused in the description herein and throughout the claims that follow,“a”, “an”, and “the” include plural references unless the contextclearly dictates otherwise. Also as used in the description herein andthroughout the claims that follow, the meaning or “in” includes “in” and“on” unless the context clearly dictates otherwise.

The foregoing description of illustrated embodiments of the presentinvention, including what is described in the summary or in theabstract, is not intended to be exhaustive or to limit the invention tothe precise forms disclosed herein. From the foregoing, it will beobserved that numerous variations, modifications and substitutions areintended and may be effected without departing from the spirit and scopeof the novel concept of the invention. It is to be understood that nolimitation with respect to the specific methods and apparatusillustrated herein is intended or should be inferred. It is, of course,intended to cover by the appended claims all such modifications as fallwithin the scope of the claims.

1. An apparatus for providing current independently to a series of lightemitting diodes of a plurality of series of light-emitting diodes, theapparatus comprising: a power converter couplable to the plurality ofseries of light-emitting diodes, the power converter adapted to generatea current; a first multiplexer couplable to the plurality of series oflight-emitting diodes; and a controller coupled to the power converterand to the first multiplexer, the controller adapted to provide forsequential and separate switching of the current through the firstmultiplexer to each of the series of light-emitting diodes, of theplurality of series of light-emitting diodes, for a corresponding periodof time.
 2. The apparatus of claim 1, wherein the controller is furtheradapted to provide for no switching of current through the firstmultiplexer to all remaining series of light-emitting diodes whilecurrent is switched to a selected series of light-emitting diodes of theplurality of series of light-emitting diodes.
 3. The apparatus of claim1, wherein the controller is further adapted to determine an averagecurrent provided by the power converter as about equal to a sum of aplurality of corresponding currents through the plurality of series oflight-emitting diodes.
 4. The apparatus of claim 3, wherein thecontroller is further adapted to determine a total period for switchingcurrent to all of the series of light-emitting diodes of the pluralityof series of light-emitting diodes.
 5. The apparatus of claim 4, whereinthe controller is further adapted to determine a corresponding timeperiod for switching current to a selected corresponding series oflight-emitting diodes as substantially equal to a proportion of thetotal period determined as a ratio of the corresponding current for theselected corresponding series of light-emitting diodes to the averagecurrent provided by the power converter.
 6. The apparatus of claim 1,further comprising: a memory coupled to the controller, the memoryadapted to store, as a look up table, a plurality of-parameterscorresponding to the plurality of series of light-emitting diodes. 7.The apparatus of claim 6, wherein the controller is further adapted topredict an output voltage across a selected series of light-emittingdiodes based on the device parameters stored in memory and to revise thepredicted output voltage based upon a measured output voltage across aselected series of light-emitting diodes.
 8. The apparatus of claim 1,wherein the power converter further comprises a first voltage divider,and wherein the controller is further adapted to determine an inputvoltage across the first voltage divider.
 9. The apparatus of claim 1,wherein the power converter further comprises a current sensor, andwherein the controller is further adapted to determine a peak inputcurrent through the current sensor.
 10. The apparatus of claim 1,further comprising a plurality of second voltage dividers, each secondvoltage divider couplable in parallel to a corresponding series oflight-emitting diodes of the plurality of series of light-emittingdiodes, and wherein the controller is further adapted to determine acorresponding output voltage across the corresponding second voltagedivider of the plurality of second voltage dividers.
 11. The apparatusof claim 10, further comprising: a second multiplexer coupled to theplurality of second voltage dividers and the controller, and wherein thecontroller is further adapted to control switching of the secondmultiplexer to a selected second voltage divider of the plurality ofsecond voltage dividers.
 12. The apparatus of claim 1, furthercomprising: a third multiplexer couplable to the plurality of series oflight-emitting diodes and coupled to the controller, and wherein thecontroller is further adapted to control switching of the thirdmultiplexer to a selected series of light-emitting diodes of theplurality of series of light-emitting diodes for measuring acorresponding current through the selected series of light-emittingdiodes.
 13. The apparatus of claim 12, wherein the controller is furtheradapted to determine the corresponding period of time for switching ofcurrent to a selected series of light-emitting diodes based on acomparison of the measured corresponding current to a predeterminedcurrent level for the selected series of light-emitting diodes.
 14. Theapparatus of claim 1, wherein the first multiplexer further comprises: aplurality of switches, each switch of the plurality of switchescorrespondingly couplable to a first, high side of a correspondingseries of light-emitting diodes of the plurality of series oflight-emitting diodes.
 15. The apparatus of claim 1, wherein the firstmultiplexer further comprises: a plurality of switches, each switch ofthe plurality of switches correspondingly couplable to a second, lowside of a corresponding series of light-emitting diodes of the pluralityof series of light-emitting diodes.
 16. The apparatus of claim 1,wherein the first multiplexer further comprises: a plurality of firstswitches, each switch of the plurality of first switches correspondinglycouplable to a first, high side of a corresponding series oflight-emitting diodes of the plurality of series of light-emittingdiodes; and a plurality of second switches, each switch of the pluralityof second switches correspondingly couplable to a second, low side of acorresponding series of light-emitting diodes of the plurality of seriesof light-emitting diodes.
 17. The apparatus of claim 1, furthercomprising: a plurality of capacitors, each capacitor of the pluralityof capacitors couplable to a corresponding series of light-emittingdiodes of the plurality of series of light-emitting diodes.
 18. Theapparatus of claim 17, wherein the first multiplexer further comprises:a plurality of first switches, each switch of the plurality of firstswitches correspondingly couplable to a first, high side of acorresponding series of light-emitting diodes of the plurality of seriesof light-emitting diodes; and a second switch couplable to the pluralityof capacitors.
 19. The apparatus of claim 1, wherein the controller isfurther adapted to determine the corresponding period of time forswitching of current to a selected series of light-emitting diodes basedon an integer multiple of a period of switching of the power converter.20. The apparatus of claim 1, wherein the controller is further adaptedto control switching of the first multiplexer to a selected series oflight-emitting diodes of the plurality of series of light-emittingdiodes when current through the power converter is substantially zero.21. The apparatus of claim 1, wherein the controller is further adapted,in response to a first input, to adjust an output brightness of theplurality of series of light-emitting diodes by modifying eachcorresponding period of time of current switching to each of the seriesof light-emitting diodes.
 22. The apparatus of claim 1, wherein thecontroller is further adapted, in response to a second input, to adjustan output color of the plurality of series of light-emitting diodes bymodifying at least one corresponding period of time of current switchingto at least one of the series of light-emitting diodes of the pluralityof series of light-emitting diodes.
 23. A lighting system, comprising: aplurality of series of light-emitting diodes; a power converter coupledto the plurality of series of light-emitting diodes, the power converteradapted to generate a current; a first multiplexer coupled to theplurality of series of light-emitting diodes; and a controller coupledto the power converter and to the first multiplexer, the controlleradapted to provide for sequential and separate switching of the currentthrough the first multiplexer to each of the series of light-emittingdiodes, of the plurality of series of light-emitting diodes, for acorresponding period of time.
 24. The system of claim 23, wherein thecontroller is further adapted to provide for no switching of currentthrough the first multiplexer to all remaining series of light-emittingdiodes while current is switched to a selected series of light-emittingdiodes of the plurality of series of light-emitting diodes.
 25. Thesystem of claim 23, wherein the controller is further adapted todetermine an average current provided by the power converter assubstantially equal to a sum of a plurality of corresponding currentsthrough the plurality of series of light-emitting diodes.
 26. The systemof claim 25, wherein the controller is further adapted to determine atotal period for switching current to all of the series oflight-emitting diodes of the plurality of series of light-emittingdiodes.
 27. The system of claim 26, wherein the controller is furtheradapted to determine a corresponding time period for switching currentto a selected corresponding series of light-emitting diodes assubstantially equal to a proportion of the total period determined as aratio of the corresponding current for the selected corresponding seriesof light-emitting diodes to the average current provided by the powerconverter.
 28. The system of claim 23, further comprising: a memorycoupled to the controller, the memory adapted to store, as a look uptable, a plurality of parameters corresponding to the plurality ofseries of light-emitting diodes.
 29. The system of claim 28, wherein thecontroller is further adapted to predict an output voltage across aselected series of light-emitting diodes based on the device parametersstored in memory and to revise the predicted output voltage based upon ameasured output voltage across a selected series of light-emittingdiodes.
 30. The system of claim 23, wherein the power converter furthercomprises a first voltage divider, and wherein the controller is furtheradapted to determine an input voltage across the first voltage divider.31. The system of claim 23, wherein the power converter furthercomprises a current sensor, and wherein the controller is furtheradapted to determine a peak input current through the current sensor.32. The system of claim 23, further comprising a plurality of secondvoltage dividers, each second voltage divider coupled in parallel to acorresponding series of light-emitting diodes of the plurality of seriesof light-emitting diodes, and wherein the controller is further adaptedto determine a corresponding output voltage across the correspondingsecond voltage divider of the plurality of second voltage dividers. 33.The system of claim 32, further comprising: a second multiplexer coupledto the plurality of second voltage dividers and the controller, andwherein the controller is further adapted to control switching of thesecond multiplexer to a selected second voltage divider of the pluralityof second voltage dividers.
 34. The system of claim 23, furthercomprising: a third multiplexer coupled to the plurality of series oflight-emitting diodes and to the controller, and wherein the controlleris further adapted to control switching of the third multiplexer to aselected series of light-emitting diodes of the plurality of series oflight-emitting diodes for measuring a corresponding current through theselected series of light-emitting diodes.
 35. The system of claim 34,wherein the controller is further adapted to determine the correspondingperiod of time for switching of current to a selected series oflight-emitting diodes based on a comparison of the measuredcorresponding current to a predetermined current level for the selectedseries of light-emitting diodes.
 36. The system of claim 23, wherein thefirst multiplexer further comprises: a plurality of switches, eachswitch of the plurality of switches correspondingly coupled to a first,high side of a corresponding series of light-emitting diodes of theplurality of series of light-emitting diodes.
 37. The system of claim23, wherein the first multiplexer further comprises: a plurality ofswitches, each switch of the plurality of switches correspondinglycoupled to a second, low side of a corresponding series oflight-emitting diodes of the plurality of series of light-emittingdiodes.
 38. The system of claim 23, wherein the first multiplexerfurther comprises: a plurality of first switches, each switch of theplurality of first switches correspondingly coupled to a first, highside of a corresponding series of light-emitting diodes of the pluralityof series of light-emitting diodes; and a plurality of second switches,each switch of the plurality of second switches correspondingly coupledto a second, low side of a corresponding series of light-emitting diodesof the plurality of series of light-emitting diodes.
 39. The system ofclaim 23, further comprising: a plurality of capacitors, each capacitorof the plurality of capacitors coupled to a corresponding series oflight-emitting diodes of the plurality of series of light-emittingdiodes.
 40. The apparatus of claim 39, wherein the first multiplexerfurther comprises: a plurality of first switches, each switch of theplurality of first switches correspondingly coupled to a first, highside of a corresponding series of light-emitting diodes of the pluralityof series of light-emitting diodes; and a second switch coupled to theplurality of capacitors.
 41. The system of claim 23, wherein thecontroller is further adapted to determine the corresponding period oftime for switching of current to a selected series of light-emittingdiodes based on an integer multiple of a period of switching of thepower converter.
 42. The system of claim 23, wherein the controller isfurther adapted to control switching of the first multiplexer to aselected series of light-emitting diodes of the plurality of series oflight-emitting diodes when current through the power converter issubstantially zero.
 43. The system of claim 23, wherein the controlleris further adapted, in response to a first input, to adjust an outputbrightness of the plurality of series of light-emitting diodes bymodifying each corresponding period of time of current switching to eachof the series of light-emitting diodes.
 44. The system of claim 23,wherein the controller is further adapted, in response to a secondinput, to adjust an output color of the plurality of series oflight-emitting diodes by modifying at least one corresponding period oftime of current switching to at least one of the series oflight-emitting diodes of the plurality of series of light-emittingdiodes.
 45. A method of selectively and independently providing power toa series of light emitting diodes of a plurality of series oflight-emitting diodes, the method comprising: generating an input DCcurrent having a first average level; and sequentially and separatelyswitching the DC current to each of the series of light-emitting diodes,of the plurality of series of light-emitting diodes, for a correspondingperiod of time.
 46. The method of claim 45, further comprising:switching no current to all remaining series of light-emitting diodeswhile switching the DC current to a selected series of light-emittingdiodes of the plurality of series of light-emitting diodes.
 47. Themethod of claim 45, further comprising: determining the first averagelevel of DC current as substantially equal to a sum of a plurality ofcorresponding currents through the plurality of series of light-emittingdiodes.
 48. The method of claim 47, further comprising: determining atotal period for switching current to all of the series oflight-emitting diodes of the plurality of series of light-emittingdiodes.
 49. The method of claim 48, further comprising: determining acorresponding time period for switching current to a selectedcorresponding series of light-emitting diodes as substantially equal toa proportion of the total period determined as a ratio of thecorresponding current for the selected corresponding series oflight-emitting diodes to the average current provided by the powerconverter.
 50. The method of claim 45, further comprising: storing, as alook up table, a plurality of parameters corresponding to the pluralityof series of light-emitting diodes.
 51. The method of claim 50, furthercomprising: predicting an output voltage across a selected series oflight-emitting diodes, of the plurality of series of light-emittingdiodes, based on the stored device parameters.
 52. The method of claim51, further comprising: measuring a corresponding output voltage foreach series of light emitting diodes of the plurality of series oflight-emitting diodes.
 53. The method of claim 52, further comprising:updating the predicted output voltage across a selected series oflight-emitting diodes, of the plurality of series of light-emittingdiodes, based on a corresponding measured output voltage.
 54. The methodof claim 45, further comprising: determining an input voltage.
 55. Themethod of claim 45, further comprising: determining a peak input DCcurrent.
 56. The method of claim 45, further comprising: determining acorresponding output voltage for each series of light emitting diodes ofthe plurality of series of light-emitting diodes.
 57. The method ofclaim 45, further comprising: measuring a corresponding current througheach series of light-emitting diodes of the plurality of series oflight-emitting diodes.
 58. The method of claim 45, further comprising:determining the corresponding period of time for switching of current toa selected series of light-emitting diodes based on a comparison of themeasured corresponding current to a predetermined current level for theselected series of light-emitting diodes.
 59. The method of claim 45,further comprising: determining the corresponding period of time forswitching of current to a selected series of light-emitting diodes basedon an integer multiple of a period of switching of a power converter.60. The method of claim 45, further comprising: switching current to aselected series of light-emitting diodes of the plurality of series oflight-emitting diodes when the input DC current is substantially zero.61. The method of claim 45, further comprising: in response to a firstinput, adjusting an output brightness of the plurality of series oflight-emitting diodes by modifying each corresponding period of time ofcurrent switching to each of the series of light-emitting diodes. 62.The method of claim 45, further comprising: in response to a secondinput, adjusting an output color of the plurality of series oflight-emitting diodes by modifying at least one corresponding period oftime of current switching to at least one of the series oflight-emitting diodes of the plurality of series of light-emittingdiodes.
 63. An apparatus for providing current independently to a seriesof light emitting diodes of a plurality of series of light-emittingdiodes, the apparatus comprising: a power converter couplable to theplurality of series of light-emitting diodes, the power converteradapted to generate a current; a first multiplexer couplable to theplurality of series of light-emitting diodes; a memory adapted to store,as a look up table, a plurality of parameters corresponding to theplurality of series of light-emitting diodes; and a controller coupledto the power converter, to the first multiplexer and to the memory, thecontroller adapted to provide for sequential and separate switching ofthe current through the first multiplexer to each of the series oflight-emitting diodes, of the plurality of series of light-emittingdiodes, for a corresponding period of time; the controller furtheradapted to determine an average current provided by the power converteras a substantially equal to sum of a plurality of corresponding currentsthrough the plurality of series of light-emitting diodes, to determine atotal period for switching current to all of the series oflight-emitting diodes of the plurality of series of light-emittingdiodes, and to determine a corresponding time period for switchingcurrent to a selected corresponding series of light-emitting diodes assubstantially equal to a proportion of the total period determined as aratio of the corresponding current for the selected corresponding seriesof light-emitting diodes to the average current provided by the powerconverter.
 64. The apparatus of claim 63, wherein the controller isfurther adapted to predict an output voltage across a selected series oflight-emitting diodes based on the device parameters stored in memoryand to revise the predicted output voltage based upon a measured outputvoltage across a selected series of light-emitting diodes.
 65. Theapparatus of claim 63, further comprising: a plurality of second voltagedividers, each second voltage divider couplable in parallel to acorresponding series of light-emitting diodes of the plurality of seriesof light-emitting diodes; a second multiplexer coupled to the pluralityof second voltage dividers and the controller; and wherein thecontroller is further adapted to control switching of the secondmultiplexer to a selected second voltage divider of the plurality ofsecond voltage dividers and to determine a corresponding output voltageacross the corresponding second voltage divider of the plurality ofsecond voltage dividers.
 66. The apparatus of claim 63, furthercomprising: a third multiplexer couplable to the plurality of series oflight-emitting diodes and coupled to the controller; and wherein thecontroller is further adapted to control switching of the thirdmultiplexer to a selected series of light-emitting diodes of theplurality of series of light-emitting diodes for measuring acorresponding current through the selected series of light-emittingdiodes.
 67. The apparatus of claim 63, wherein the controller is furtheradapted to determine the corresponding period of time for switching ofcurrent to a selected series of light-emitting diodes based on acomparison of the measured corresponding current to a predeterminedcurrent level for the selected series of light-emitting diodes.
 68. Theapparatus of claim 63, wherein the controller is further adapted todetermine the corresponding period of time for switching of current to aselected series of light-emitting diodes based on an integer multiple ofa period of switching of the power converter.
 69. The apparatus of claim63, wherein the controller is further adapted, in response to a firstinput, to adjust an output brightness of the plurality of series oflight-emitting diodes by modifying each corresponding period of time ofcurrent switching to each of the series of light-emitting diodes. 70.The apparatus of claim 63, wherein the controller is further adapted, inresponse to a second input, to adjust an output color of the pluralityof series of light-emitting diodes by modifying at least onecorresponding period of time of current switching to at least one of theseries of light-emitting diodes of the plurality of series oflight-emitting diodes.